Is your worm bin outside? If so, don't worry too much about the snails, since if they're able to find your worm bin, they're also able to find your garden. You won't be delivering any extra threat to your garden that isn't there already.

Parsley, I have never seen such snails in my garden. There are larger ones and slugs but not this tiny snails variety-I must have added them with some kitchen scraps :-( The worms bin is outside on the porch - I doubt that snails could get through the dry tile and into the bin - they usually like damp places.